A variable pitch fan in this specification means a plurality of circumferentially arranged blades mounted for rotation about one axis and rotatable about their longitudinal axes to vary their angle of attack as they rotate about the one axis.
Variable pitch fan mechanisms which have developed out of the variable pitch propeller technology have suffered from heaviness and complexity and therefore, as exemplified in the U.S. Pat. to McMurtry et at, No. 3,825,370, dated July 23, 1974, effort has been made to develop lighter and simpler variable pitch fan mechanisms. Additionally, heretofore known variable pitch fan mechanisms including the mechanism of the aforementioned patent, have had the disadvantage of recirculating power losses resulting from fan torque load feed-back through the pitch-changing gear train during the long periods of steady state operation (no blade pitch-change).
It is, therefore, one of the objects of this invention to provide a variable pitch mechanism for fan blades which is relatively light in weight and relatively simple in construction.
Another object of the present invention is to provide a variable pitch mechanism for fan blades in which recirculating power losses are eliminated.
A still further object of this invention is to provide a variable pitch mechanism for fan blades where the differential gear train of such mechanism runs unloaded during steady state operation.